Cores for casting concrete beams



United States Patent [72] Inventor Richard E. Herro Joliet, Ill.

[21] Appl. No. 718,589

[22] Filed Apr; 3, 1968 {45] Patented Dec. 29, 1970 [73] AssignceDearhorn Rubber Corporation Broadview, III.

a corporation of Illinois [54] CORES FOR CASTING CONCRETE BEAMS 2Claims, 4 Drawing Figs.

2,312,587 3/1943 Price 2,395,216 2/1946 Fitzpatrick ABSTRACT: Aremovable core for forming an axial opening in concrete beams includesan elongated hollow tubular core member or body formed of elastomericmaterial, together with end caps for sealing the ends of the body andmeans for pressurizing the interior of the body during the concretecasting process. The body in cross section includes a square outerperiphery so that the amount of concrete required to form a beam isreduced. The body maintains its square shape when pressurized withoutthe use of reinforcing or supporting structure. In one arrangement, thewalls of the body are ofsubstantially equal thickness throughout and arebowed inwardly at the sides of the square. In another arrangement, theinner wall of the body is circular so that upon pressurization there isno tendency for the square outer shape to be distorted.

[52] [1.8. C] 249/178, 25/41, 25/128 B281) 7/32 [50] 25/ 128D, 4165A;249/65, 178, 179, 183,134;18/RMD, Cone positioning, expansible mold;25/ho1low block, rubber matrix [56] References Cited UNITED STATESPATENTS 2,153,741 4/1939 Cobi 25/154 32 I" l .EHI Z 1 I I/ L 1 I I I" li e T l 38 l I l l l -|il ull/ll CORES FOR CASTING CONCRETE BEAMS Thepresent invention relates to pores for use in casting hollow concretemembers such as beams, slabs and the like.

In the manufacture of prestressed concrete beams, one widely usedprocedure is to cast a concrete beam having a central longitudinalopening extending the length of the beam. After the concrete has set,tendons such as cables, wires or rods passing through the beam aretensioned thereby to subject the beam to compressive stress. In thepast, hollow beams have been formed by using cores which are expanded orpressurized while the concrete is setting and which are contracted ordepressurized and removed from the beam thereafter.

A known type of core includes an elongated, circular cylindrical tubehaving a wall formed of a flexible material such as rubber. The tube isplaced within a mold for-the beam and the tube is enveloped withconcrete when the mold is filled. The

,tube is pressurized while the concrete sets so that it maintains itsshape and does not collapse under the weight of the concrete. When theconcrete is strong enough to retain its shape without internal supportthe tube is deflated and removed from the beam. This type of core hasthe important advantages of simplicity and low cost.

It has also been proposed to use a core having a polygonal rather than around outer shape. A square configuration, for

example, provides a saving in material cost by reducing the 1 amount ofconcrete used in the beam, and does not substantially reduce thestrength of the finished beam. In the past it has not been possible touse a simple'square tube formed of 1 rubber or the like and constructedalong the lines of the round tubes used in the past because whenpressurized such a square tube is forced into a rounded shape. Becauseof this difficulty, square cores developed to date have been subject tothe disadvantages of complexity and high cost due to the inclusion of.structure required to support or reinforce the core in order to assurethattlie square shape is maintained when the core is concrete beams orthe like including an elongated hollow tubular core member or bodyformed of an elastomeric material and having a polygonal outer peripheryin cross section. The

ends of the body are sealed, and means are provided for admitting apressurizing medium such as air to the interior of the body. Inaccordance with an important feature of the inven tion, the body isformed entirely of the elastomeric material and does not include anyother supporting or reinforcing structure. Rather, the body isconstructed to maintain its polygonal outer shape when pressurizedwithout the necessity for any additional support.

In one embodiment of the invention, the tendency of the body to .becomeround upon pressurization is counteracted by forming an inward bow orconcavity into its sides. In another arrangement, the inner surface ofthe body is circular in cross .section while the outer surface ispolygonal. Upon pressurization, there is no tendency for the outer shapeto become distorted or rounded.

' The invention and its objects and advantages may be better understoodfrom the following detailed description wherein reference is made to theaccompanying drawing in which:

FIG. 1 is a fragmentary, elevational view, partly in section,

3 of a core embodying features of the present invention;

FIG. 2 is an enlarged, sectional view taken along the line I 2-2ofFIG.1;

FIG. 3 is a fragmentary, elevational, sectional view, on a reducedscale, of part ofthe core of FIG. 1; and

FIG. 4 is a view similar to FIG. 2 illustrating an alternativeembodiment of the present invention.

Referring now to the drawing and initially to FIGS. I and 2 there isillustrated a core constructed in accordance with the present inventionand designated as a whole by the reference numeral 10. The core 10 isused in a process of casting hollow concrete beams and in generalincludes a central, hollow core member or body generally designated as12, the ends of which are sealed by cap members 14 and 16. Cap 14 isprovided with a valve assembly 18 of known construction so that apressurizing medium such as pressurized air can be admitted to andreleased from the core member 12.

In use, the core 10 is supported within a mold into which concrete ispoured in order to cast a beam. The core is surrounded by concrete, andin order to prevent the core member from collapsing under the weight ofthe concrete, it is pressurized by admitting a pressurizing medium toits interior through the valve assembly 18. The core remains pressurizedwhile the concrete sets, and thereafter the pressure is relieved byopening the valve assembly 18. The core is then pulled from the concreteto reveal a tunnellike opening or passage through the beam.

In accordance with an important aspect of the present invention the coremember 12, although extremely simple and therefore inexpensive toconstruct, is generally square in shape and is capable of retaining itssquare shape when pressurized. The square shape gives rise to a savingin material cost since less concrete is required as compared with a beamformed around a circular core having a diameter. equal to a side of thesquare. Furthermore, as compared with such a round core the square shapedoes not substantially detract from the strength of the beam. It shouldbe appreciated that nonround shapes other than square are within thescope of the present invention. Although the advantages of a square coreare widely appreciated, the present invention provides a simple corecapable of retaining a square shape without the use of complexsupporting and reinforcing structure heretofore thought necessary with apressurized, nonrigid core.

In accordance with one feature of the invention the core member 12 isable to maintain its square shape when pressurized because in itsrelaxed, unpressurized state the sides of the core member are concave orbowed inwardly. The core member 12 is shown in its relaxed state in FIG.2 where the inward bow or concavity is indicated by the dimension a. Theinward bowing of the sides of the core member counteracts the tendencyof the core member to become rounded or distorted when subjected tointernal pressure. When the core member is pressurized, the wall 12a ofthe core member is deformed to some extent, but this deformation merelystraightens the walls and in fact results in the core member becomingmore square rather than less square. 7

Another aspect of the invention contributing to the abilit of the coremember 12 to remain in a substantially square shape when pressurized isthe choice of material used. In accordance with the invention, thematerial should be flexible enough so that the body can be deformedslightly when=pressurized. However, the material should exhibit thecharacteristic of stiffness to the extent that the deformation of thesides of the core member is limited so that the sides do not becomeappreciably convex when the core member is pressurized. Furthermore, thematerial should be resilient so that when the pressure within the coreis relieved the member 12 reverts to its original shape and can beremoved from the concrete beam. One material which has been found to besuitable in all these respects and which is also advantageously light inweight is a low density polyethylene. By way of example, and withoutlimiting the scope of the invention, suitable materials are a lowdensity semirigid polyethylene identified as Number 0224 sold by UnionCarbide and Carbon Corp., and a material sold under the trademarkTenite," Number 860, and available from Tennessee Eastman Company. a

One important and heretofore unobtainable advantage 0 the core of thepresent invention is the: simplicity of the core member 12 and the easewith which it can be fabricated. Thus the core member may be formed of asingle, homogeneous material throughout and may have a uniform crosssection throughout its length. In addition, the core member may have awall of uniform thickness throughout. Accordingly the core member may beentirely formed in a simple and inexpensive extrusion operation,although other methods could be used to form the core member.

It will be appreciated that in practical embodiments of the invention,the core member may be of substantial length, and for this reason thecore has been illustrated in broken form in FIG. 1. As shown in FIG. 3,where long lengths are required two or more members 12 may be splicedtogether by means of a sleeve cemented inside the abutting ends. Thecore may be supplied in a variety of sizes ranging for example from 4 to12 inches in width and in lengths up to 60 feet or more. The degree ofinward bow indicated by the dimension a in FIG. 2 may vary with the sizeof the core member and also with the material used in the core. By wayof example, in a core member having a 4-inch width and made of lowdensity polyethylene an inward bow of one thirty-second inch may beused.

Proceeding to a more detailed description of the cap members l4 and 16,the cap 14 includes a body 22 from which extends a pluglike projection24 snuggly received with the end of the core member 12. A pair ofrecesses 26 and 28 in the cap 14 are separated by a wall 220 and areselectively intercommunicated by the valve assembly 18. A bail or ring30 is supported on the cap 14 permitting the core 10 to be pulled from abeam after setting of the concrete.

Sealing of the other end of the core member 12 is accomplished by meansof the cap member 16 which includes a body 32 and a pluglike projection34 received within the core member 12. In order securely to seal the endof the member 12, a gasket 36 is expanded against the inner wall of themember 12 by an eye bolt 38 threaded into a compression plate 40.

Referring now to FIG. 4, there is illustrated another embodiment of thepresent invention. This figure illustrates in cross section a coremember embodying important features of the invention and generallydesignated as 50. 1t should be understood that although cap members arenot illustrated for the core member 50, they may be similar to the capmembers 14 and 16 used with the core member 12 described above.

In accordance with a feature of the invention, the core member 50 issimple in shape and is inexpensive to construct but is nevertheless ableto retain a square or other nonround outer shape when pressurized,without the necessity for reinforcing or supporting structure. This isaccomplished by providing the core member 50 with a generally squareouter wall 50a and a circular inner wall 50b. When pressurized, due tothe provision of the circular inner wall 50b, there is no tendency forthe shape of the square outer wall 50a to become distorted. l

The core member 50 may also be fabricated inexpensively from a single,homogeneous material in an extrusion process. Any desired elastomericmaterial such as rubber or the like may be used. Cap members for thecore member 50 may be identical to the members 14 and 16 except thattheir projecting plug portions would be round to fit within the circularinner wall 50b.

While the present invention has been described in connection with thedetails of illustrative embodiments thereof, other embodiments andmodifications may be devised by those skilled in the art which fallwithin the spirit and scope of the invention. The details of thedescribed embodiments should not be taken to limit the invention exceptinsofar as set forth in the following claims.

lclaim:

1. A core for use in casting hollow concrete beams or the likecomprising an elongated hollow tubular body formed of a flexibleextruded rubber material, means for sealing the ends of said body, andmeans for admitting a pressurizing medium to the interior of said body,said body in cross section having a substantially rectangular outerperiphery and having a substantially circular inner periphery so thatthe shape of the outer periphery is maintained upon pressurization ofthe body.

2. The core of claim 1, said outer periphery being square.

